How to insert a new record with Foreign key?

Database:

In User_Monhoc table, user_id is a foreign key. I need insert 1 new record into User_Monhoc (with user_id is a exists record in User).

User_Monhoc Map:

<hibernate-mapping>
    <class name="entites.UserMonhoc" table="user_monhoc" catalog="bthibernate" optimistic-lock="version">
        <composite-id name="id" class="entites.UserMonhocId">
            <key-property name="userId" type="string">
                <column name="user_id" length="100" />
            </key-property>
            <key-property name="mhId" type="string">
                <column name="mh_id" length="100" />
            </key-property>
        </composite-id>
        <many-to-one name="monhoc" class="entites.Monhoc" update="false" insert="false" fetch="select">
            <column name="mh_id" length="100" not-null="true" />
        </many-to-one>
        <many-to-one name="user" class="entites.User" update="false" insert="false" fetch="select">
            <column name="user_id" length="100" not-null="true" />
        </many-to-one>
    </class>
</hibernate-mapping>

My code:

private final SessionFactory sf = HibernateUtil.getSessionFactory();

public boolean InsertStudent(String idUS, String idMH) {
    try {
        String xxxx = "";
        String hql2 = "INSERT INTO User_Monhoc(user_id,mh_id,tuan1, tuan2, tuan3, tuan4, tuan5, tuan6, tuan7, tuan8, tuan9, tuan10, tuan11, tuan12, tuan13, tuan14, tuan15) VALUES('" + idUS + "','" + idMH + "', 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0 )";
        System.out.println(hql2);

        Query query = sf.getCurrentSession().createSQLQuery(hql2);
        int cc = query.executeUpdate();

        System.out.println(cc + "Dong");
        sf.getCurrentSession().getTransaction().commit();

        return true;
    } catch (Exception e) {
        return false;
    }
}

Error mesage:

org.hibernate.HibernateException: createSQLQuery is not valid without active transaction